The present invention relates to color picture tubes having improved inline electron guns and particularly to such guns using a tube neck coating as one of the gun electrodes.
An inline electron gun is one designed to generate or initiate preferably three electron beams in a common plane and direct those beams along convergent paths to a point or small area of convergence near the tube screen. In one type of inline electron gun, shown in U.S. Pat. No. 3,873,879, issued to R. H. Hughes on Mar. 25, 1975, the main electrostatic focusing lens for focusing the electron beams is formed between two electrodes referred to as the first and second accelerating and focusing electrodes. These electrodes include two cup-shaped members having their bottoms facing each other. Three apertures are included in each cup bottom to permit passage of three electron beams and to form three separate main focus lenses, one for each electron beam. In a preferred embodiment, the overall diameter of the electron gun is such that the gun will fit into a 29 mm tube neck. Because of this size requirement, the three focusing lenses are very closely spaced from each other, thereby providing a severe limitation on focus lens design. It is known in the art that the larger the focus lens diameter, the lesser will be the spherical aberration which restricts the focus quality.
One means of obtaining a larger focus lens is to use an internal coating on the tube neck as the final focus electrode. Such internal coating was used commercially in single beam monochrome tubes. Internal coating electrodes of multibeam shadow mask color picture tubes are disclosed in the following U.S. Pat. Nos.
______________________________________ U.S. Pat. No. Inventor Issued ______________________________________ 2,714,176 Friend July 26, 1955 2,726,347 Benway Dec. 6, 1955 2,726,348 Benway Dec. 6, 1955 2,861,208 Benway Nov. 18, 1958 3,011,090 Moodey Nov. 28, 1961 3,024,380 Burdick et al. Mar. 6, 1962 ______________________________________
Although, apparently, considerable work was done on these multibeam tubes, such tubes were never commercially developed.
The present invention utilizes an internal coating electrode in novel combination with other electron gun features to provide an electron gun of the inline beam type which has lower focus lens aberration than other inline electron guns.